If your drawers look anything like mine, (and yes, my drawers are very messy all the time) it can be an overwhelming thing to start. Just pick a drawer or end of the closet and go through every single thing you've got- even if that means dumping everything on the floor and sorting through it piece by piece! 

My bed usually turns into the give away pile, the floor for the need to be thrown out pieces that are stained or have holes and my closet/ drawers for the keepers! A good rule to keep in mind is if you haven't worn it in 6-8 months it's no longer something you need. The only exception to this is your simple dresses, and seasonal jackets. Everything else can go. 

Purging your closet also gives you the perfect opportunity to reorganize what you've got. I like to group my tees, tanks, long sleeves & dresses into sections so I can easily find what I am looking for when getting ready! Depending on what you have for space, you can decide how you want to organize everything. I usually keep my clothes rack for all tops and dresses, and my bottoms go into my chest of drawers with my pjs and workout wear. 

Before anything gets given away, I toss it in the laundry to make sure it's clean before it gets given to anyone else and then I just pile everything up and put it in a blue garbage bag. So easy. If I don't have a specific person that I am giving my clothes to, I'll stop by a Goodwill donation centre and drop everything there!